A fuel cell is a device that produces electricity by converting chemical energy from a fuel into electrical energy through an electrochemical reaction within a fuel cell stack, instead of converting the chemical energy from the fuel into heat through combustion. Fuel cells may provide power for industries, households, and vehicles, and may also be applied to power supply for small electric/electronic products, especially, portable devices.
Currently, proton exchange membrane fuel cells (PEMFCs), also known as polymer electrolyte membrane fuel cells, having the highest power density among fuel cells are being studied as a power source for driving vehicles. The PEMFCs have a rapid startup time and a quick power conversion response time due to a low operating temperature. Such a PEMFC includes: a membrane electrode assembly (MEA) having catalyst electrode layers, in which an electrochemical reaction occurs, attached to both sides of a solid polymer electrolyte membrane through which hydrogen ions move; gas diffusion layers (GDLs) serving to uniformly distribute reactant gases and deliver electrical energy that is generated; gaskets and coupling members for maintaining air tightness of the reactant gases and a coolant and appropriate clamping pressure; and bipolar plates allowing the reactant gases and the coolant to move therethrough.
When such unit cells are assembled to form a fuel cell stack, a combination of main components, MEA and GDL, is positioned in the innermost portion of the cell. The MEA includes the catalyst electrode layers, i.e., an anode and a cathode with a catalyst coated on both surfaces of the polymer electrolyte membrane to allow hydrogen and oxygen to react with each other. The GDLs, the gaskets, and the like are stacked on the anode and the cathode in the outer portion of the cell. The bipolar plates having respective flow fields formed therein are positioned outwardly of the GDLs, the flow fields supplying the reactant gases (e.g., hydrogen as a fuel and oxygen or air as an oxidizing agent) and allowing the coolant to pass therethrough.
After the plurality of unit cells having the above-described configuration are stacked, current collectors, insulating plates, and end plates for supporting the stacked cells are combined in the outermost portion of the stack. The unit cells are repeatedly stacked and assembled between the end plates to form the fuel cell stack. To obtain an electric potential required in a vehicle, it is necessary to stack the number of unit cells corresponding to the required amount of electric potential energy, and the stacked unit cells are called a stack. For example, an electric potential generated from a single unit cell is about 1.3V, and to generate power required for driving a vehicle, the plurality of cells may be stacked in series.
Such a fuel cell stack suffers from deterioration as the driving time, mileage, and the frequency of starting of a vehicle are increased. However, this is not a temporary deterioration resulting from a dry or flooding state, but deterioration in the membrane of the stack itself, which may reduce the output of the fuel cell stack to lower fuel-efficiency and limit the launching performance of the vehicle. Conventionally, when the fuel cell stack suffers from deterioration, part of the cells within the fuel cell stack are repaired or replaced to recover the performance thereof. Such a conventional method may be a fundamental solution, but the disassembly and assembly of the fuel cell stack consumes a lot of time and incurs replacement costs.